Prioritize reveal clipping over Outline clipping

bug:15780987
bug:17350602

Also update docs around clipping nesting behavior,
and some Z ordering behavior.

Change-Id: Iaa204350a0adfdcbd8c4b821fb4a9c0ae22f2613
diff --git a/libs/hwui/StatefulBaseRenderer.h b/libs/hwui/StatefulBaseRenderer.h
index c6974b4..745e48a 100644
--- a/libs/hwui/StatefulBaseRenderer.h
+++ b/libs/hwui/StatefulBaseRenderer.h
@@ -97,7 +97,7 @@
      */
     void setClippingOutline(LinearAllocator& allocator, const Outline* outline);
     void setClippingRoundRect(LinearAllocator& allocator,
-            const Rect& rect, float radius);
+            const Rect& rect, float radius, bool highPriority = true);
 
     inline const mat4* currentTransform() const {
         return mSnapshot->transform;